Dynamic Analysis Of Pile-fermentation Process For Pu-erh Tea At Different Seasons

Based on the initial exploration of pile-fermentation for Pu-erh tea on laboratory-scale,the dynamic changes of microorganism, enzyme activity and physicochemical properties ofPu-erh teas during pile-fermentation were investigated in the present study, and aromacharacteristics, catechin composition and antioxidant activity of sample fermented at differentseasons had also been analyzed. This information will be useful to improve thepile-fermentation process for Pu-erh tea.Results showed that there was no significant difference in mould amount at variousinitial moisture contents, yeast of30%group was significant less than others at final stage.Polyphenol oxidase (PPO) of35%group had significant higher enzyme activity than others.At final stage, protease activity of45%group was significant lower than the level of rawmaterials while others were opposite. The activity of amylase, cellulose and pectinasedecreased significantly at the initial moisture content lower than the the critical level of40%.The PCR-DGGE results suggested that Aspergillus niger was dominant microbe at initialstage, then Arxula adeninivorans became dominant fungi in intermediate and final stages.Bacillus was dominant bacteria at final stage of the fermentation.The results of L9(33) orthogonal experiment showed that mould and enzyme activitiesremained at high level with initial moisture content at the range of40%to45%. Theadjustment of pH of the tea pile had no effect on the mould and enzyme activities. Mouldremained at high level by turning per8days and enzyme activities remained at high level byturning per6days. Based on the contents of theabrownin, tea polyphenol and catechins, itcould be concluded that Pu-erh tea would be excessive oxidated by high level initial moisturecontent (50%) and too high or too low turning frequency(4d,8d).Seasonal factor on the pile-fermentation of Pu-erh tea was further studied. Higher roomtemperature was unfavored in mould growth, and high humidity could inhibit bacteria to someextent. However, little effect of seasonal factor on the yeast was observed. There was asignificant correlation between the mould and polyphenol oxidase, protease, cellulose and pectinase, indicating that pile-fermentation was influenced by mould through secretion ofextracellular enzymes. Yeast and bacteria were significant negatively correlated withcatechins, tea polyphenols, theaflavins, thearubigins, soluble sugars and amino acids, andsignificant positively correlated with total flavonoids, theabrowns and water extracts,indicating that yeast and bacteria had also significant effect on characteristic components ofPu-erh tea.The content of gallic acid was increasing by33.98%,17.69%,15.43%and38.62%respectively, the largest was found in winter sample. All kinds of catechins were reduced invarying degrees, C and EGC could hardly be detected, and other ingredients were also onmicroscale.Solid phase micro extraction coupled with gas chromatography-mass spectrometry wereused to determine aroma. Terpenol alcohols were the main aroma components in raw tea,while methoxy-phenolic compounds and terpenol derivatives were major classes in ripe teas.The stale and mouldy fiavour of Pu-erh tea came from methoxy-phenolic compounds. Thecontent of methoxy-phenolic compounds varied in ripe teas fermented at different seasons,which amounted to38.613%and28.579%respectively for winter sample and summer sample.1,2,3-trimethoxybenzene, the main volatile aroma composition in ripe teas, which was alsofound highest in winter sample (21.157%) and lest in summer sample (14.000%). The higherpercentage of methoxy-phenolic compounds provide a theoretical basis for stronger stale andmouldy flavour in winter sample.Antioxidant activity was evaluated by total antioxidant capacity, reducing power, DPPHradical and hydroxyl radical scavenging ability. The results indicated that raw tea had strongerantioxidant activity than ripe teas. Winter sample showed better antioxidant activity thanothers except for reducing power, indicating that winter sample had the best function amongripe teas fermented at different seasons.